A man walks through debris as the Japanese national flag flies on June 12, 2011, in Otsuchi, Iwate, Japan.

A rapid rise in radiation levels reportedly forced officials at Japan's stricken Fukushima Dai-ichi nuclear power plant to halt efforts Saturday to clean contaminated water just hours after the operation started.

Fresh water has been being pumped into the plant to cool damaged reactors. About 100,000 tons of highly radioactive water -- enough to fill 40 Olympic-sized swimming pools -- has built up during the process, the BBC reports.

The water risks overflowing within a few weeks if action is not taken soon, the Associated Press reports.

The Fukushima plant was crippled when an earthquake and tsunami devastated much of Japan March 11. The disaster knocked out the plant's cooling systems, sparking meltdowns and radiation leaks.

A spokesman for the Tokyo Electric Power Co (TEPCO), which runs the plant, told the AP the cause of the rise in radiation is being investigated. The spokesman, Junichi Matsumoto, did not say when the operation would resume.

"We do not have a firm timing as to when we can resume the operation of the water treatment facility," Matsumoto told a news conference, as reported by AFP.

A water treatment system began its full operations Friday, but the plant suspended it Saturday when workers found a sharp radiation increase in the system's caesium-absorbing component, AP states.

A plant operator told AFP that a new part was needed to resume the operation.

Officials said the part of the system that absorbs the caesium needs to be replaced earlier than expected because it has reached its processing capacity, AFP states.

The water in the plant must be decontaminated before it can be stored or recycled back through the reactors. Once the water is pumped out, workers should be able to repair the cooling systems.

TEPCO plans to bring the reactors to a stable cold shutdown state by next January.